This invention relates generally to a method and apparatus for controlling the steering of a tracked machine and, more particularly, to a method and apparatus for controlling the direction of a tracked machine as the machine travels on a straight line path.
Tracked machines, such as track-type tractors, skid steer loaders, and the like, are used to perform a variety of work functions under conditions which require an amount of traction not available with conventional wheeled machines. The tracked machines typically are driven by some type of differential transmission system, which applies the driving force to each of a left and a right track. Generally, the tracked machines are steered by controlling the speed of each track; that is, if it is desired to turn to the left, the left track is made to move slower compared to the right track to effectuate the turn. If it is desired to move the tracked machine along a straight line path, i.e., straight tracking the machine, both tracks are made to move at equal speeds.
A problem that exists, however, is that it is often difficult, if not impossible, to keep both tracks at the same speed, particularly under load conditions. One track may periodically slip, thus causing the machine to deviate from its straight line path. An operator must constantly be aware of this situation, and must frequently make steering corrections to keep the machine traveling in the desired direction.
A common method employed to monitor straight tracking of a tracked machine, and possibly provide automated steering adjustments, is to employ speed sensors at each track to sense any speed differentials between tracks. However, this requires two sensors, which must be installed at locations which are highly prone to adverse conditions, such as dirt, mud, rocks, and the like. Consequently, inaccuracies and even failure of these speed sensors are fairly common.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention a method for controlling straight line travel of a tracked machine having a left track and a right track is disclosed. The method includes the steps of initiating a straight line travel mode of the tracked machine, determining an initial heading angle of a heading sensor located on the tracked machine, sensing a deviation in heading angle from the initial heading angle as the tracked machine travels, determining a heading angle error in response to the deviation in heading angle, and adjusting the speed of at least one of the left and right tracks to compensate for the heading angle error. In another aspect of the present invention an apparatus for automatically controlling straight line travel of a tracked machine having a left track and a right track is disclosed. The apparatus includes a steering control mechanism located on the tracked machine for initiating a straight line travel mode in response to being set to a neutral position, a heading sensor located on the tracked machine for determining an initial heading angle of the tracked machine in response to initiation of the straight line travel mode, and for determining a deviation in heading angle from the initial heading angle as the tracked machine travels, and a controller located on the tracked machine for determining a heading angle error in response to the deviation in heading angle, and for adjusting the speed of at least one of the left and right tracks to compensate for the heading angle error.